This invention relates to spinnerets with orifices for improved filament cross-sections, and more particularly for spinning filaments of improved cross-sections that have multiple longitudinal grooves in the periphery of the filament cross-sections.
Some 40 years ago, Pamm and Rogers disclosed in U.S. Pat. No. 2,816,349 that pill-resistant fabrics could be made from melt-spun synthetic staple of denier per filament no more than about 1.6 and a filament ratio (modification ratio) of at least about 5, suitable filaments being prepared by melt-spinning through an essentially slot-shaped orifice, having a width no greater than about 2 mils (50 microns), abruptly expanded tips and additional abrupt expansions separating every 10 to 20 mils (250 to 500 microns) of slot length, slots being substantially rectangular with length 5 or more times their width, and the expanded tips and additional abrupt expansions being preferably circular, but could be rectangular, square, diamond shaped or oval, provided that the longer dimensions of the non-circular embodiments be approximately perpendicular to the length of the slot. Lehmicke, in U.S. Pat. No. 2,945,739, disclosed essentially similar spinneret orifices and that such designs in the form of a Y, a T, a cross, a spiral and the like were possible. Their intention was to spin filaments of high filament ratio (modification ratio) such as having cross-sections of length to width ratio 5 or more.
Multi-lobed filaments have been described, e.g. by Strachan some 30 years ago in U.S. Pat. No. 3,156,607, Gorrafa some 20 years ago in U.S. Pat. No. 3,914,488, Franklin and Clark et al. some 10 years later in U.S. Pat. Nos. 4,634,625 and 4,707,407, respectively, and more recently Toray (Tsukamoto et al.) in Japanese Patent Application Kokai Hei 4-119118, published Apr. 20, 1992. Strachan disclosed filament cross-sections of essentially oval cross-section (A:B ratio 1.3 to 1.8) and having 6 to 8 lobes with tip radius ratios of 0.15 to 0.6 and interconnected by smooth continuous peripheral lines that were xe2x80x9cfree from abrupt changes of directionxe2x80x9d. Strachan spun his filaments from slotted orifices having configurations as shown in his FIG. 7 for 6 lobes, and in his FIG. 8 for 8 lobes, and the tip radius ratio was controlled by varying the width of the slots or by providing circular apertures at their extremities as shown in his FIG. 9. Toray (Japanese Hei 4-119118) disclosed a somewhat similar 8-lobed oval deformed cross-section for his filament in his FIG. 1, spun from a slotted spinneret orifice shown in his FIG. 2, in which a longer central vertical slot was provided in contrast to shorter vertical slots on either side; spinneret slot dimensions were not disclosed by Toray. Gorrafa, Franklin and Clark et al. all disclosed filaments having cross-sections that are now referred to as scalloped-oval cross-sections, A:B ratios being 1.4:1 to 2.4:1, with tip radius ratios being disclosed and 4 grooves also being disclosed. Gorrafa showed two spinneret orifice configurations: his FIG. 5 was used to spin his filaments of his Example 1, and the orifice comprised 3 diamond-shaped holes that were separated but closely-spaced to permit melt coalescence after extrusion; his FIG. 6 was used to spin his filaments of his Example 2, and these orifices comprised 3 round holes interconnected by 2 channels; Gorrafa disclosed his spinneret orifice dimensions in his Examples; his objective was to make pile fabrics from his filaments to simulate natural furs. Franklin claimed new woven fabrics with yarns that had been textured from partially-oriented feed yarns whose filaments had the scalloped-oval cross-section. Franklin used spinneret orifices as shown in his FIG. 2, said to be 3 diamond-shaped units joined by slots; spinneret orifice dimensions were not disclosed by Franklin. Clark""s disclosure of spinneret orifices was similar to Franklin""s, but Clark made water-dispersible fiber of short cut length.
About 15 years ago, Minemura et al. disclosed in U.S. Pat. No. 4,316,924 synthetic furs with guard hair-like raised synthetic fibers as disclosed in a Japanese Patent Publication No. 48-4910 of dpf 10 to 100 and having transverse cross-sections with at least one constricted part as shown, for example, in Minemura""s FIGS. 1A to 1S, obtained by using spinnerets having orifices as shown in FIGS. 2A to 2S.
As indicated in the art, it has proved difficult in practice to design spinneret orifice configurations that provide filaments of fine dpf and having multiple grooves that extend along the length of the filaments and yet avoid processing problems, such as fibrillation, i.e., separation of the portions of the filaments by tearing along the groove during spinning or during later processing of the filaments. This is the problem that faced the present inventors and has been solved by them.
Accordingly, there is provided a spinneret for the production of multi-grooved filaments, comprising a plate having upper and lower surfaces connected by a capillary, said capillary being defined at the lower surface by a complex orifice that comprises a plurality of apertures, said apertures having flow areas (A), said apertures being located in a row, said apertures having widths (H) in a direction that is perpendicular to said row, and said apertures being interconnected by slots that are also located in said row, said slots having flow areas (a) and widths (h), said widths (h) also being in a direction that is perpendicular to said row, wherein sizes of flow areas A and a are such that the ratio a/A for an aperture and for a slot adjacent thereto is about 0.02:1 to about 0.2:1, and widths H and h are such that the ratio h/H for an aperture and for a slot adjacent thereto is about 0.05:1 to about 0.25:1.
The apertures should preferably not all be circular, but most should be of greater width than a circle, i.e., should extend away from the row of slots to a greater extent, and are preferably diamond-shaped, for instance as shown in FIGS. 1, 2 or 4 referred to herein, but may be of other non-round shapes, such as shown for example in FIG. 5 herein.
In preferred spinnerets, the width (H) of an aperture at an end of the row is less than the width (H) of an aperture between the ends of the row, especially such as to produce a multi-grooved filament of generally scalloped-oval periphery with multiple indentations, i.e., grooves in the periphery, such as may be obtained, for example, by spinning filaments from orifices as shown in FIG. 1 or FIG. 4.